Modern aircraft power generation systems often use variable frequency generators (VFGs). The VFGs are designed to carry required overloads at the lowest operating speeds of the VFGs. This results in the generator having a higher capacity at the highest operating speeds. As a result of this design consideration, some faults in a generator control unit or the generator can cause significant over voltages at higher operating speeds if the faults are not identified quickly.
To protect against such faults, fast trip protection devices are included in the generator and trip whenever an overvoltage is present. Due to the fast nature of the fast trip protection devices, it is also possible for nuisance trips to occur. A nuisance trip occurs when a fault is present in the load and the fast trip protection device falsely detects a fault in the generator. When a nuisance trip occurs, it is imprudent to disconnect the generator from the load and connect an alternate power source.